"nano" vs "pico" vs "femto" accelerometers?

Totally new to ST accelerometers, I can see that they're grouped into what look like three "families" -- nano, pico and femto. Is there a short explanation of the differences between those three families? A link to a page explaining that would be just ducky, thanks.

If they're just marketing terms, then it's a bit confusing for the product summary sheet to seem to emphasize that categorization so prominently. If I look at, say, the page for the LIS2DW12, LIS2DW12 - MEMS digital output motion sensor:high-performance ultra-low-power 3-axis "femto" accelerometer - STMicroelec… , I am told in the first few lines that this item is a member of the "femto" family. But without a definition of what that means, then telling me that information is useless and even confusing, since the first thing I thought of when I read that is, "What does 'femto' mean? Am I supposed to already understand that? Is there a glossary that explains it? Is 'femto' better than 'pico'?"

Unless there's a page that explains the difference between those families, there's absolutely no marketing value in mentioning it.